Electromagnetic vibration exciter system with adjustable electro-viscoelastic suspension device

ABSTRACT

The electromagnetic vibration exciter system with an adjustable electro-viscoelastic suspension device comprises an electromagnetic vibration exciter, a power amplifier and an adjustable electro-viscoelastic suspension device, which acts as the suspension device of the electromagnetic vibration exciter. The adjustable electro-viscoelastic suspension device contains a displacement sensor detecting the displacement of the moving component, a first adjustable amplifier and a second adjustable amplifier, a differentiator, an adjustable phase shifter, an adder and a proportioner. The linearity of the stiffness and damping of the exciter system is excellent, which can be adjusted as need through the adjustment of gain of the adjustable amplifier, the proportioner, the adjustable phase shifter. This invention has adjustable and linear parameters and it is also easy to be realized.

This is a U.S. national stage application of PCT Application No.PCT/CN2012/075025 under 35 U.S.C. 371, filed May 3, 2012 in Chinese,claiming the priority benefit of Chinese Application No. 201110113959.2,filed May 4, 2011, which is hereby incorporated by reference.

FIELD OF THE INVENTION

This present invention relates to an electromagnetic vibration excitersystem with an adjustable electro-viscoelastic suspension device.

BACKGROUND OF THE INVENTION

The electromagnetic vibration exciter usually comprises a fixed base, amagnetic circuit, a moving component, a guiding device, a suspensionsystem and so on. With the development of the science and technology,the electromagnetic exciters are constantly required to output avibration signal with a larger and larger displacement amplitude. Forexample, at a low frequency or even an ultralow frequency, the excitershould output a vibration signal with the displacement amplitude of 1000mm in order to obtain a large signal-to-noise ratio. The long-strokevibration exciter raises new requirement for the property of the elasticsuspension device.

An electromagnetic vibration exciter generally uses mechanical elasticsuspension devices, such as metal spring leaf or rubber tubes, etc. tosupport and restore the moving component. When the operating stroke ofthe exciter is relatively small, the mechanical elastic suspensiondevice operates in a linear zone, whose effect on the accuracy of theoutput waveform of the exciter is negligible. When the operating strokeof the exciter is relatively large (for example, when working at anultralow frequency up to 0.01 Hz, the exciter could output a vibrationsignal with the displacement amplitude of up to 1000 mm), the mechanicalelastic suspension device will exhibit relatively large nonlinearcharacteristics, which will have a relatively large impact on theexciter performance. Besides, the larger the displacement amplitude ofthe exciter is, the smaller the stiffness of the mechanical elasticsuspension device should be. However, in order to reduce the effect ofthe zero drift of the moving component and the environmental noise, thedampness of the suspension device should be relatively large. It isdifficult to design such type of mechanical elastic suspension devicewith small stiffness and large dampness. In addition, due to that thematerial characteristics of the mechanical elastic suspension devicechange always with time, the positional accuracy cannot be repeatable.Finally, when the installation of the mechanical elastic suspensiondevice is finished, its stiffness and damping parameters cannot bemodified freely any more. For these reasons, the mechanical elasticsuspension device cannot meet the requirement arisen with the continuousdevelopment of electromagnetic exciters, especially for the long-strokeelectromagnetic exciter.

SUMMARY OF THE INVENTION

To overcome the above shortcomings of the prior art, the presentinvention provides a novel electromagnetic vibration exciter system withan adjustable electro-viscoelastic suspension device. Such suspensiondevice has the function of a traditional mechanical device but with thestiffness and damping parameters that can be adjusted easily accordingto actual requirements. The present invention has an excellent linearquality even for a long-stroke vibration, which results in significantimprovement of the performance of the novel electromagnetic exciter.

The electromagnetic vibration exciter system with an adjustableelectro-viscoelastic suspension device comprises an electromagneticexciter and a power amplifier;

Its characteristics are as follow. The adjustable electro-viscoelasticsuspension device is adopted in the vibration exciter system to supportand restore its moving component and comprises a displacement sensordetecting the displacement of the moving component of theelectromagnetic exciter, a first adjustable amplifier, a secondadjustable amplifier, a differentiator, an adder and an adjustable phaseshifter, a subtracter, a proportioner.

The displacement signal detected by the sensor is processed by the firstadjustable amplifier and a first amplified signal is produced. Thedisplacement signal is simultaneously processed by the differentiatorand the second adjustable amplifier successively and a second amplifiedsignal is produced. The first amplified signal and the second amplifiedsignal are added by the adder, the output of which is processed by theadjustable phase shifter. The phase-shifted signal is imported into thesubtracter as subtrahend. Another input terminal of the subtracter isconnected with the signal generator, the standard output of which is theminuend. The subtracter output is imported into the proportioner, theoutput of which is amplified by the power amplifier and then is importedinto the exciter as the driving signals.

In addition, the transfer function of the proposed exciter system is asfollow:

$\begin{matrix}\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{3}{K_{p} \cdot \frac{Bl}{\begin{matrix}{{mLs}^{3} + {\left( {{mR} + {c_{2}L}} \right)s^{2}} +} \\{{\left\lbrack {{Rc}_{2} + ({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}} \right\rbrack s} + {K_{1}K_{3}K_{4}K_{p}{Bl}}}\end{matrix}}}}} \\{= {\frac{K_{3}K_{p}{Bl}}{R} \cdot \frac{1}{\begin{matrix}{{\frac{m\; L}{R}s^{3}} + {\left( {m + \frac{c_{2}L}{R}} \right)s^{2}} +} \\{{\left\lbrack {c_{2} + \frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}} \right\rbrack s} + \frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}}\end{matrix}}}}\end{matrix} & (1)\end{matrix}$where m is the total mass of the moving component (including thevibration table and the load under excitation); c₂ is the damping causedby other factors than the suspension device, such as air damping; B isthe magnetic flux density in the air gap; l is the length of the coilwithin the magnetic field; L and R are the inductance and resistance ofthe coil respectively; K₁, K₂, K₃, K₄ and K_(P) is the gain of the firstadjustable amplifier, the second adjustable amplifier, the proportioner,the adjustable phase shifter and the power amplifier, respectively; s=jωis the Laplace operator; ω is the circular frequency of the vibration.

$C = {c_{2} + \frac{{({Bl})^{2} + {K_{2}\; K_{3}\; K_{4}\; K_{p}\;{Bl}}}\mspace{11mu}}{R}}$in (1) reflects the equivalent damping characteristic of the system;

$K = \frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}$reflects its equivalent stiffness characteristic; c₂ is mainly caused byair damping;

$\frac{K_{2}K_{3}K_{4}K_{p}{Bl}}{R}\operatorname{>>}c_{2}$can be true if K₂, K₃, K₄ are adjusted properly and

${C \approx \frac{{({Bl})^{2} + {K_{2}\; K_{3}\; K_{4}\; K_{p}\;{Bl}}}\mspace{11mu}}{R}};$B is assumed as constant independent with the displacement of the movingcomponent x; Then the damping factor C and the stiffness factor K bothkeep as constant and could be adjusted easily as need through theadjustment of K₁, K₂, K₃, K₄.

In addition, the transfer function of the exciter system running at thelow and ultralow frequency is as follow:

$\begin{matrix}\begin{matrix}{{G(s)}\; = \frac{X(s)}{U(s)}} \\{= {K_{3}\;{K_{P} \cdot \frac{Bl}{\begin{matrix}{{mRs}^{2}\; + \;{\left\lbrack {{Rc}_{2}\; + \;{K_{2}\; K_{3}\; K_{4}\; K_{P}\;{Bl}}\; + \;({Bl})^{2}} \right\rbrack\; s}\; +} \\{K_{1}\; K_{3}\; K_{4}\; K_{P}\;{Bl}}\end{matrix}\;}}}} \\{= {\frac{K_{3}\;{K_{P} \cdot {Bl}}}{R} \cdot \frac{1}{\begin{matrix}{{{m\; s^{2}}\; + \;{\left\lbrack {c_{2}\; + \;\frac{{K_{2}\; K_{3}\; K_{4}\; K_{P}\;{Bl}}\; + \;({Bl})^{2}}{R}} \right\rbrack\; s}\; +}\;} \\\frac{K_{1}\; K_{3}\; K_{4}\; K_{P}\;{Bl}}{R}\end{matrix}}}}\end{matrix} & (2)\end{matrix}$where

$C = {c_{2} + \frac{{({Bl})^{2} + {K_{2}\; K_{3}\; K_{4}\; K_{p}\;{Bl}}}\mspace{11mu}}{R}}$in (2) reflects the equivalent damping characteristic of the system;

$K = \frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}$reflects its equivalent stiffness characteristic; c₂ is mainly caused byair damping;

$\frac{K_{2}K_{3}K_{4}K_{p}{Bl}}{R}\operatorname{>>}c_{2}$can be true if K₂, K₃, K₄ are adjusted properly and

${C \approx \frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}};$B is assumed as constant independent with the displacement of the movingcomponent x; Then the damping factor C and the stiffness factor K bothkeep as constant. The system thus has good linear characteristics.Through the adjustment of the gain of the adjustable amplifier, theadjustable phase shifter and the proportioner, the equivalent stiffnessfactor K and damping factor C of the suspension system of the excitercan be directly adjusted.

The technical consideration of present invention is to replace theuncontrollable, nonlinear mechanical suspension device with thecontrollable, linear and precise electrical device. The displacementsignal of the exciter is processed by the proportioner and thedifferentiator and then is fed back into the exciter system to realizethe function of former mechanical suspension device.

The electromagnetic vibration exciter usually comprises a fixed base, amagnetic circuit, a moving component, a guiding device, and a suspensionsystem and so on. The traditional mechanical elastic suspension devicebased on metal spring leaf or rubber belt, etc. is often applied tosupport and restore the moving component. The moving component iscomposed of a coil, a coil skeleton and a vibration table, the three ofwhich are well connected. Its first-order modal frequency is more thanfive times as the maximum working frequency and it can be seen as arigid body. Then the electromagnetic vibration exciter can be simplifiedas a single-degree-of-freedom model. Meanwhile take into considerationof the electrical equation of the driving coil and the equationreflecting the electromechanical coupling relation can be expressed as

$\begin{matrix}\left\{ \begin{matrix}{{{m\overset{¨}{x}} + {c\overset{.}{x}} + {kx}} = {Bli}} \\{{{L\frac{\mathbb{d}i}{\mathbb{d}t}} + {Ri} + {{Bl}\overset{.}{x}}} = u_{0}}\end{matrix} \right. & (3)\end{matrix}$where m is the total mass of the moving component (including thevibration table and the load under excitation); k and c is the stiffnessand damping of the moving component respectively, c=c₁+c₂, c₁ is causedby the mechanical suspension device and c₂ is caused by other factors,such as air damping; B is the magnetic flux density in the air gap; l isthe length of the coil within the magnetic field; L and R is theinductance and resistance of the coil respectively; i is the currentflowing in the coil; u₀ is the driving voltage applied between the twoends of the coil; x is the displacement of the vibration table.

Then the transfer function of traditional vibration exciter is expressedas

$\begin{matrix}\begin{matrix}{{G_{2}(s)} = \frac{X(s)}{U_{0}(s)}} \\{= \frac{Bl}{{mLs}^{3} + {\left( {{mR} + {cL}} \right)s^{2}} + {\left\lbrack {{Rc} + ({Bl})^{2} + {kL}} \right\rbrack s} + {Rk}}}\end{matrix} & (4)\end{matrix}$

Traditional vibration exciter system comprises an exciter and a poweramplifier with the transfer function of G₁(s)=K_(p). Then the transferfunction of the traditional vibration exciter system is expressed as

$\begin{matrix}\begin{matrix}{{G_{2}(s)} = \frac{X(s)}{U(s)}} \\{= {K_{p} \cdot \frac{Bl}{{mLs}^{3} + {\left( {{mR} + {cL}} \right)s^{2}} + {\left\lbrack {{Rc} + ({Bl})^{2} + {kL}} \right\rbrack s} + {Rk}}}} \\{= {\frac{K_{p}{Bl}}{R} \cdot \frac{1}{{\frac{m\; L}{R}s^{3}} + {\left( {m + \frac{cL}{R}} \right)s^{2}} + {\left\lbrack {c + \frac{({Bl})^{2} + {kL}}{R}} \right\rbrack s} + k}}}\end{matrix} & (5)\end{matrix}$where K_(p) is gain of the power amplifier.

$C = {c + \frac{({Bl})^{2} + {kL}}{R}}$in (5) reflects the equivalent damping characteristic of the system; K=kreflects the equivalent stiffness characteristic. K and C cannot beadjusted easily after the installation and contains nonlinear factors kand c, which results in the nonlinearity of K and C.

The mechanical suspension device is removed in present invention. Sok=0, c=c₂, and the electromechanical coupling equation is shown as

$\begin{matrix}\left\{ \begin{matrix}{{{m\overset{¨}{x}} + {c_{2}\overset{.}{x}}} = {Bli}} \\{{{L\frac{\mathbb{d}i}{\mathbb{d}t}} + {Ri} + {{Bl}\overset{.}{x}}} = u_{0}}\end{matrix} \right. & (6)\end{matrix}$where c₂ is mainly caused by the air damping. Then the transfer functionof the exciter is

$\begin{matrix}\begin{matrix}{{G_{2}(s)} = \frac{X(s)}{U_{0}(s)}} \\{= \frac{Bl}{{mLs}^{3} + {\left( {{mR} + {c_{2}L}} \right)s^{2}} + {\left\lbrack {{Rc}_{2} + ({Bl})^{2}} \right\rbrack s}}}\end{matrix} & (7)\end{matrix}$

Meanwhile, an adjustable electro-viscoelastic suspension device isadopted, which is realized as follow.

The displacement signal x detected by a displacement sensor is processedby a first adjustable amplifier with gain of K₁ and a first amplifiedsignal is produced. The displacement signal x is simultaneouslyprocessed by a differentiator and a second adjustable amplifier withgain of K₂ successively and a second amplified signal is produced. Thefirst amplified signal and the second amplified signal are added by anadder, the output of which is processed by an adjustable phase shifterwith gain of K₄ and phase shift of φ. Then the output of the phaseshifter is subtracted as subtrahend by the standard output of a signalgenerator, and the difference is processed by a proportioner with gainof K₃ and then is amplified by a power amplifier with gain of K_(P) asfollow. The output of the power amplifier is imported into the exciteras the driving signals in the end.

Then the transfer function of the feedback unit isG ₃(s)=(K ₁ +K ₂ s)·K ₄ e ^(−jφ)  (8)Assuming that the phase shift of the adjustable phase shifter φ=0, thenG ₃(s)=(K ₁ +K ₂ s)·K ₄  (9)The transfer function of the power amplifier and the proportioner areG₁(s)=K_(p) and G₄(s)=K₃ respectively, then the transfer function of thewhole exciter system with the electro-viscoelastic suspension device is

$\begin{matrix}\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{3}{K_{p} \cdot \frac{Bl}{\begin{matrix}{{mLs}^{3} + {\left( {{mR} + {c_{2}L}} \right)s^{2}} +} \\{{\left\lbrack {{Rc}_{2} + ({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}} \right\rbrack s} + {K_{1}K_{3}K_{4}K_{p}{Bl}}}\end{matrix}}}}} \\{= {\frac{K_{3}K_{p}{Bl}}{R} \cdot \frac{1}{\begin{matrix}{{\frac{m\; L}{R}s^{3}} + {\left( {m + \frac{c_{2}L}{R}} \right)s^{2}} +} \\{{\left\lbrack {c_{2} + \frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}} \right\rbrack s} + \frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}}\end{matrix}}}}\end{matrix} & (10)\end{matrix}$where

$C = {c_{2} + \frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}}$in (10) reflects the equivalent damping characteristic of the system;

$K = \frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}$reflects its equivalent stiffness characteristic;

$\frac{K_{2}K_{3}K_{4}K_{p}{Bl}}{R}\operatorname{>>}c_{2}$can be true if K₂, K₃, K₄ are adjusted properly and

$C \approx {\frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}.}$Compared with C and K in (5), the two factors here are irrelevant withnonlinear factors k and c. B is assumed as a constant independent withthe displacement of the moving component x, then the damping factor Cand the stiffness factor K both keep as constant and could be adjustedeasily as need through the adjustment of K₁, K₂, K₃ and K₄.

Especially,

$\frac{\mathbb{d}i}{\mathbb{d}t}$is negligible for the low-frequency and ultralow-frequency vibration andit can be assumed that

$\frac{\mathbb{d}i}{\mathbb{d}t}$in (3) is equal to zero, then the electromechanical coupling equation oftraditional electromagnetic exciter changes to be

$\begin{matrix}\left\{ \begin{matrix}{{{m\overset{¨}{x}} + {c\overset{.}{x}} + {kx}} = {Bli}} \\{{{Ri} + {{Bl}\overset{.}{x}}} = u_{0}}\end{matrix} \right. & (11)\end{matrix}$Accordingly, the transfer function of traditional exciter system is

$\begin{matrix}\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{p} \cdot \frac{Bl}{{mRs}^{2} + {\left\lbrack {{Rc} + ({Bl})^{2}} \right\rbrack s} + {Rk}}}} \\{= {\frac{K_{p}{Bl}}{R} \cdot \frac{1}{{m\; s^{2}} + {\left( {c + \frac{({Bl})^{2}}{R}} \right)s} + k}}}\end{matrix} & (12)\end{matrix}$Such system can be seen as a typical single-degree-of-freedom model. Theequivalent damping and stiffness are

$C = {c + \frac{({Bl})^{2}}{R}}$and K=k respectively. K and C cannot be adjusted easily after theinstallation completion and contain nonlinear factors k and c, whichresult in the nonlinearity of K and C.

The electromechanical equation (6) of traditional electromagneticexciter removing the mechanical suspension device changes to be

$\begin{matrix}\left\{ \begin{matrix}{{{m\overset{¨}{x}} + {c_{2}\overset{.}{x}}} = {Bli}} \\{{{Ri} + {{Bl}\overset{.}{x}}} = u_{0}}\end{matrix} \right. & (13)\end{matrix}$Then the transfer function of the exciter system applying theelectro-viscoelastic suspension device changes to be

$\begin{matrix}\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{3}{K_{P} \cdot \frac{Bl}{{mRs}^{2} + {\left\lbrack {{Rc}_{2} + {K_{2}K_{3}K_{4}K_{P}{Bl}} + ({Bl})^{2}} \right\rbrack s} + {K_{1}K_{3}K_{4}K_{P}{Bl}}}}}} \\{= {\frac{K_{3}{K_{P} \cdot {Bl}}}{R} \cdot \frac{1}{\begin{matrix}{{m\; s^{2}} + {\left\lbrack {c_{2} + \frac{{K_{2}K_{3}K_{4}K_{P}{Bl}} + ({Bl})^{2}}{R}} \right\rbrack s} +} \\\frac{K_{1}K_{3}K_{4}K_{P}{Bl}}{R}\end{matrix}}}}\end{matrix} & (14)\end{matrix}$Such system can also be seen as a typical single-degree-of-freedommodel. The equivalent damping and stiffness are

$C = {c_{2} + {\frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{P}{Bl}}}{R}\mspace{14mu}{and}}}$$K = \frac{K_{1}K_{3}K_{4}K_{P}{Bl}}{R}$respectively. c₂ is mainly caused by air damping;

$\frac{K_{2}K_{3}K_{4}K_{p}{Bl}}{R}\operatorname{>>}c_{2}$can be true if K₂, K₃, K₄ are adjusted properly and

$C \approx {\frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}.}$Assuming B is a constant independent with the displacement of the movingcomponent x, then the equivalent damping factor C and the stiffnessfactor K in function (14) both keep as constant and the system hasexcellent linear characteristics and the performance of the system canbe improved. Comparing functions (12) and (14), it can be clearly seenthat, through the adjustment of the gain of the adjustable amplifier,the adjustable phase shifter and the proportioner, the equivalentdamping factor C and the stiffness factor K can be directly adjusted.

To solve the phase shift between the input voltage and outputdisplacement signal of the exciter appearing at high working frequency,the adjustable phase shifter can be adjusted to ensure that the phase ofthe feedback signal and the standard signal remains consistent.

The present invention has the advantage of parameter adjustable, linearand convenience.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a dynamic model of the moving component in the electromagneticvibration exciter.

FIG. 2 is an electromechanical coupling model of the electromagneticvibration exciter.

FIG. 3 is a model of the exciter system with traditional mechanicalsuspension device.

FIG. 4 is a structure of the present invention.

FIG. 5 is a model of the exciter system with the adjustableelectro-viscoelastic suspension device.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings.

The electromagnetic vibration exciter system with an adjustableelectro-viscoelastic suspension device comprises an electromagneticvibration exciter and a power amplifier.

The adjustable electro-viscoelastic suspension device is adopted in thevibration exciter system to support and restore its moving component andcomprises a displacement sensor detecting the displacement of the movingcomponent of the electromagnetic exciter, a first adjustable amplifier,a second adjustable amplifier, a differentiator, an adder and anadjustable phase shifter, a subtracter, a proportioner.

The displacement signal detected by the sensor is processed by the firstadjustable amplifier and a first amplified signal is produced. Thedisplacement signal is simultaneously processed by the differentiatorand the second adjustable amplifier successively and a second amplifiedsignal is produced. The first amplified signal and the second amplifiedsignal are added by the adder, the output of which is processed by theadjustable phase shifter. The phase-shifted signal is imported into thesubtracter as subtrahend. Another input terminal of the subtracter isconnected with the signal generator, the standard output of which is theminuend. The subtracter output is imported into the proportioner, theoutput of which is amplified by the power amplifier and then is importedinto the exciter as the driving signals.

The technical consideration of present invention is to replace theuncontrollable, nonlinear mechanical suspension device with thecontrollable, linear and precise electrical device. The displacementsignal of the exciter is processed by the proportioner and thedifferentiator and then is fed back into the exciter system to realizethe function of former mechanical suspension device.

The electromagnetic vibration exciter usually comprises a fixed base, amagnetic circuit, a moving component, a guiding device, and a suspensionsystem and so on. The traditional mechanical elastic suspension devicebased on metal spring leaf or rubber belt, etc. is often applied tosupport and restore the moving component. The moving component iscomposed of a coil, a coil skeleton and a vibration table, the three ofwhich are well connected. Its first-order modal frequency is more thanfive times as the maximum working frequency and it can be seen as arigid body. Then the electromagnetic vibration exciter can be simplifiedas a single-degree-of-freedom model as shown in FIG. 1. Meanwhile takeinto the consideration of the electrical equation of the driving coiland the equation reflecting the electromechanical coupling relationshown in FIG. 2 can be expressed as

$\begin{matrix}\left\{ \begin{matrix}{{{m\overset{¨}{x}} + {c\overset{.}{x}} + {kx}} = {Bli}} \\{{{L\frac{\mathbb{d}i}{\mathbb{d}t}} + {Ri} + {{Bl}\overset{.}{x}}} = u_{0}}\end{matrix} \right. & (1)\end{matrix}$where m is the total mass of the moving component (including thevibration table and the load under excitation); k and c is the stiffnessand damping of the moving component respectively, c=c₁+c₂, c₁ is causedby the mechanical suspension device and c₂ is caused by other factors,such as air damping; B is the magnetic flux density in the air gap; l isthe length of the coil within the magnetic field; L and R is theinductance and resistance of the coil respectively; i is the currentflowing in the coil; u₀ is the driving voltage applied between the twoends of the coil; x is the displacement of the vibration table.

Then the transfer function of traditional vibration exciter is expressedas

$\begin{matrix}\begin{matrix}{{G_{2}(s)} = \frac{X(s)}{U_{0}(s)}} \\{= \frac{Bl}{{mLs}^{3} + {\left( {{mR} + {cL}} \right)s^{2}} + {\left\lbrack {{Rc} + ({Bl})^{2} + {kL}} \right\rbrack s} + {Rk}}}\end{matrix} & (2)\end{matrix}$

The model of traditional vibration exciter system is shown in FIG. 3 andthe transfer function of the power amplifier is G₁(s)=K_(p). Then thetransfer function of the traditional vibration exciter system isexpressed as

$\begin{matrix}\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{p} \cdot \frac{Bl}{{mLs}^{3} + {\left( {{mR} + {cL}} \right)s^{2}} + {\left\lbrack {{Rc} + ({Bl})^{2} + {kL}} \right\rbrack s} + {Rk}}}} \\{= {\frac{K_{p}{Bl}}{R} \cdot \frac{1}{{\frac{m\; L}{R}s^{3}} + {\left( {m + \frac{cL}{R}} \right)s^{2}} + {\left\lbrack {c + \frac{({Bl})^{2} + {kL}}{R}} \right\rbrack s} + k}}}\end{matrix} & (3)\end{matrix}$where K_(p) is gain of the power amplifier.

$C = {c + \frac{({Bl})^{2} + {kL}}{R}}$in (3) reflects the equivalent damping characteristic of the system; K=kreflects the equivalent stiffness characteristic. K and C cannot beadjusted easily after the installation and contains nonlinear factors kand c, which results in the nonlinearity of K and C.

The mechanical suspension device is removed in present invention. Sok=0, c=c₂ for (1), and the electromechanical coupling equation is shownas

$\begin{matrix}\left\{ \begin{matrix}{{{m\overset{¨}{x}} + {c_{2}\overset{.}{x}}} = {Bli}} \\{{{L\frac{\mathbb{d}i}{\mathbb{d}t}} + {Ri} + {{Bl}\overset{.}{x}}} = u_{0}}\end{matrix} \right. & (4)\end{matrix}$where c₂ is mainly caused by the air damping. Then the transfer functionof the exciter is

$\begin{matrix}{{G_{2}(s)} = {\frac{X(s)}{U_{0}(s)} = \frac{Bl}{{mLs}^{3} + {\left( {{mR} + {c_{2}L}} \right)s^{2}} + {\left\lbrack {{Rc}_{2} + ({Bl})^{2}} \right\rbrack s}}}} & (5)\end{matrix}$

Meanwhile, an adjustable electro-viscoelastic suspension device with itsstructure shown in FIG. 4 is adopted.

The displacement x signal detected by a displacement sensor is processedby a first adjustable amplifier with gain of K₁ and a first amplifiedsignal is produced. The displacement signal x is simultaneouslyprocessed by a differentiator and a second adjustable amplifier withgain of K₂ successively and a second amplified signal is produced. Thefirst amplified signal and the second amplified signal are added by anadder, the output of which is processed by an adjustable phase shifterwith gain of K₄ and phase shift of φ. Then the output of the phaseshifter is subtracted as subtrahend by the standard output of a signalgenerator, and the difference is processed by a proportioner with gainof K₃ and then is amplified by a power amplifier with gain of K_(P) asfollow. The output of the power amplifier is imported into the exciteras the driving signals in the end.

Then the adjustable electro-viscoelastic suspension device is adoptedand the model of the whole exciter system is simplified as FIG. 5. Thetransfer function of the feedback unit isG ₃(s)=(K ₁ +K ₂ s)·K ₄ e ^(−jφ)  (6)Assuming that the phase shift of the adjustable phase shift φ=0, thenG ₃(s)=(K ₁ +K ₂ s)·K ₄  (7)The transfer function of the power amplifier and the proportioner areG₁(s)=K_(p) and G₄(s)=K₃ respectively, then the transfer function of thewhole exciter system with the electro-viscoelastic suspension device is

$\begin{matrix}\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{3}{K_{p} \cdot \frac{Bl}{\begin{matrix}{{mLs}^{3} + {\left( {{mR} + {c_{2}L}} \right)s^{2}} +} \\\begin{matrix}{{\left\lbrack {{Rc}_{2} + ({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}} \right\rbrack s} +} \\{K_{1}K_{3}K_{4}K_{p}{Bl}}\end{matrix}\end{matrix}}}}} \\{= {\frac{K_{3}K_{p}{Bl}}{R} \cdot \frac{1}{\begin{matrix}\begin{matrix}{{\frac{m\; L}{R}s^{3}} + {\left( {m + \frac{c_{2}L}{R}} \right)s^{2}} +} \\{{\left\lbrack {c_{2} + \frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}} \right\rbrack s} +}\end{matrix} \\\frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}\end{matrix}}}}\end{matrix} & (8)\end{matrix}$where

$C = {c_{2} + \frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}}$in (8) reflects the equivalent damping characteristic of the system;

$K = \frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}$reflects its equivalent stiffness characteristic;

$\frac{K_{2}K_{3}K_{4}K_{p}{Bl}}{R}\operatorname{>>}c_{2}$can be true if K₂, K₃, K₄ are adjusted properly and

$C \approx {\frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}.}$Compared with C and K in (3), the two factors here are irrelevant withnonlinear factors k and c. B is assumed as a constant independent withthe displacement of the moving component x; then the damping factor Cand the stiffness factor K both keep as constant and could be adjustedeasily as need through the adjustment of K₁, K₂, K₃ and K₄.

Especially,

$\frac{\mathbb{d}i}{\mathbb{d}t}$is negligible for the low-frequency and ultralow-frequency vibration andit can be assumed that

$\frac{\mathbb{d}i}{\mathbb{d}t}$in (1) is equal to zero, then the electromechanical coupling equation oftraditional electromagnetic exciter changed to be

$\begin{matrix}\left\{ \begin{matrix}{{{m\;\overset{¨}{x}} + {c\;\overset{.}{x}} + {kx}} = {Bli}} \\{{{Ri} + {{Bl}\;\overset{.}{x}}} = u_{0}}\end{matrix} \right. & (9)\end{matrix}$Accordingly, the transfer function of traditional exciter system is

$\begin{matrix}\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{p} \cdot \frac{Bl}{{mRs}^{2} + {\left\lbrack {{Rc} + ({Bl})^{2}} \right\rbrack s} + {Rk}}}} \\{= {\frac{K_{p}{Bl}}{R} \cdot \frac{1}{{m\; s^{2}} + {\left( {c + \frac{({Bl})^{2}}{R}} \right)s} + k}}}\end{matrix} & (10)\end{matrix}$Such system can be seen as a typical single-degree-of-freedom model. Theequivalent damping and stiffness are

$C = {c + \frac{({Bl})^{2}}{R}}$and K=k respectively. K and C cannot be adjusted easily after theinstallation completion and contain nonlinear factors k and c, whichresult in the nonlinearity of K and C.

The electromechanical equation of traditional electromagnetic exciterremoving the mechanical suspension device changes to be

$\begin{matrix}\left\{ \begin{matrix}{{{m\;\overset{¨}{x}} + {c_{2}\overset{.}{x}}} = {Bli}} \\{{{Ri} + {{Bl}\;\overset{.}{x}}} = u_{0}}\end{matrix} \right. & (10)\end{matrix}$Then the transfer function of the exciter system applying theelectro-viscoelastic suspension device changes to be

$\begin{matrix}\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{3}{K_{p} \cdot \frac{Bl}{\begin{matrix}{{mRs}^{2} + {\left\lbrack {{Rc}_{2} + {K_{2}K_{3}K_{4}K_{P}{Bl}} + ({Bl})^{2}} \right\rbrack s} +} \\{K_{1}K_{3}K_{4}K_{P}{Bl}}\end{matrix}}}}} \\{= {\frac{K_{3}{K_{P} \cdot {Bl}}}{R} \cdot \frac{1}{\begin{matrix}{{m\; s^{2}} + {\left\lbrack {c_{2} + \frac{{K_{2}K_{3}K_{4}K_{P}{Bl}} + ({Bl})^{2}}{R}} \right\rbrack s} +} \\\frac{K_{1}K_{3}K_{4}K_{P}{Bl}}{R}\end{matrix}}}}\end{matrix} & (12)\end{matrix}$Such system can also be seen as a typical single-degree-of-freedommodel. The equivalent damping and stiffness are

$C = {c_{2} + {\frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{P}{Bl}}}{R}\mspace{14mu}{and}}}$$K = \frac{K_{1}K_{3}K_{4}K_{P}{Bl}}{R}$respectively. c₂ is mainly caused by air damping;

$\frac{K_{2}K_{3}K_{4}K_{p}{Bl}}{R}\operatorname{>>}c_{2}$can be true if K₂, K₃, K₄ are adjusted properly and

$C \approx {\frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}.}$Assuming B is a constant independent with the displacement of the movingcomponent x, then the equivalent damping factor C and the stiffnessfactor K in function (12) both keep as constant and the system hasexcellent linear characteristics and the performance of the system canbe improved. Comparing functions (10) and (12), it can be clearly seenthat, through the adjustment of the gain of the adjustable amplifier,the adjustable phase shifter and the proportioner, the equivalentdamping factor C and the stiffness factor K can be directly adjusted.

To solve the phase shift between the input voltage and outputdisplacement signal of the exciter appearing at high working frequency,the adjustable phase shifter can be adjusted to ensure that the phase ofthe feedback signal and the standard signal remains consistent

The specific embodiments discussed are merely illustrative of specificways to make and use the invention, and do not limit the scope of theinvention. Meanwhile, it should be appreciated that variousmodifications and their equivalents can be devised by those skilled inthe art and will fall within the spirit and scope of the principles ofthe disclosure.

The invention claimed is:
 1. An electromagnetic vibration exciter systemwith an adjustable electro-viscoelastic suspension device comprises anelectromagnetic exciter and a power amplifier; characterized in that:the adjustable electro-viscoelastic suspension device is used in thevibration exciter system to support and restore its moving component andcomprises a displacement sensor detecting displacement of the movingcomponent of the electromagnetic exciter, a first adjustable amplifier,a second adjustable amplifier, a differentiator, an adder and anadjustable phase shifter, a subtracter, and a proportioner; adisplacement detected by the sensor and a displacement signal output bythe sensor is processed by the first adjustable amplifier and a firstamplified signal is produced, the displacement signal is simultaneouslyprocessed by the differentiator and the second adjustable amplifiersuccessively and a second amplified signal is produced; the firstamplified signal and the second amplified signal are added by the adder,an output of which is processed by the adjustable phase shifter; aphase-shifted signal is imported into the subtracter as subtrahend;another input terminal of the subtracter is connected with a signalgenerator, a standard output of which is a minuend; a subtracter outputis imported into the proportioner, the output of which is amplified bythe power amplifier and then is imported into the exciter as drivingsignals; transfer function of the exciter system is as follow:$\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{3}{K_{p} \cdot \frac{Bl}{\begin{matrix}{{mLs}^{3} + {\left( {{mR} + {c_{2}L}} \right)s^{2}} +} \\{{\left\lbrack {{Rc}_{2} + ({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}} \right\rbrack s} + {K_{1}K_{3}K_{4}K_{p}{Bl}}}\end{matrix}}}}} \\{= {\frac{K_{3}K_{p}{Bl}}{R} \cdot \frac{1}{\begin{matrix}{{\frac{m\; L}{R}s^{3}} + {\left( {m + \frac{c_{2}L}{R}} \right)s^{2}} +} \\{{\left\lbrack {c_{2} + \frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}} \right\rbrack s} + \frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}}\end{matrix}}}}\end{matrix}$ where m is total mass of the moving component (including avibration table and a load under excitation; c₂ is damping caused byother factors than the suspension device; B is a magnetic flux densityin an air gap; l is length of a coil within a magnetic field; L and R isinductance and resistance of the coil respectively; K₁, K₂, K₃, K₄ andK_(P) is gain of the first adjustable amplifier, the second adjustableamplifier, the proportioner, the adjustable phase shifter and the poweramplifier, respectively; s=jω is a Laplace operator; ω is a circularfrequency of vibration;$C = {c_{2} + \frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}}$reflects equivalent damping characteristic of the system;$K = \frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}$ reflects its equivalentstiffness characteristic.
 2. The electromagnetic vibration excitersystem with an adjustable electro-viscoelastic suspension deviceaccording to claim 1, wherein the transfer function of the excitersystem running at a low and ultralow frequency is as follow:$\begin{matrix}{{G(s)} = \frac{X(s)}{U(s)}} \\{= {K_{3}{K_{P} \cdot \frac{Bl}{{mRs}^{2} + {\left\lbrack {{Rc}_{2} + {K_{2}K_{3}K_{4}K_{P}{Bl}} + ({Bl})^{2}} \right\rbrack s} + {K_{1}K_{3}K_{4}K_{P}{Bl}}}}}} \\{= {\frac{K_{3}{K_{P} \cdot {Bl}}}{R} \cdot \frac{1}{{m\; s^{2}} + {\left\lbrack {c_{2} + \frac{{K_{2}K_{3}K_{4}K_{P}{Bl}} + ({Bl})^{2}}{R}} \right\rbrack s} + \frac{K_{1}K_{3}K_{4}K_{P}{Bl}}{R}}}}\end{matrix}$ where$C = {c_{2} + \frac{({Bl})^{2} + {K_{2}K_{3}K_{4}K_{p}{Bl}}}{R}}$reflects the equivalent damping characteristic of the system;$K = \frac{K_{1}K_{3}K_{4}K_{p}{Bl}}{R}$ reflects its equivalentstiffness characteristic.